Wood Laminations and Springback

On Fri, 25 Jan 2008 02:47:56 +0000 (UTC), Bertie the Bunyip
wrote:

Stealth Pilot wrote in
:

On Wed, 23 Jan 2008 19:31:29 -0500, "Kyle Boatright"
wrote:

I'm working on the center section for a Hatz. The trailing edge of
the center section is a recurved lamination that provides better
access to the front cockpit.

I've steamed and clamped the strips into a form, and they have taken
on some of the curve, but when I unclamp 'em after they dry, I get
significant springback. The question is whether I need to allow for
this in the finished lamination, or whether the springback will go
away when I glue up the assembly?

FYI, the lamination starts as four 3" x 1/4" strips.

Thanks in advance,

Kyle Boatright

Kyle
wood is cellulose which is actually massive sugar molecules joined end
to end. joining all the cellulose together are a family of molecules
known as lignins. some lignins are thermo plastic and some are
thermosetting.
when you select wood for steaming and laminating you need to select a
timber with thermo softening lignins or you'll never get it to go soft
enough for forming.
when you've steamed a wood and placed it hot on the former then
clamped it in place until cold the wood should come off the former
with no springback. ...if it is a thermosoftening lignin.

I'd say that you've picked the wrong timber for laminating.

Spruce is what's specified in the plans. I used it and they came out of
the jig with no springback whatsoever.

Bertie

kyle steam it some more you use it. it should be too hot to handle
and pretty floppy. use leather gardening gloves.
as a guide to how small a curve can be I laminated up a bow when a
friend complained like you have.
the bow was 6" wide by 7" tall and was like a capital U.
the tighter the curve the thinner the lamination.
when wood is correctly glued is has the equivalent strength of solid
wood so dont be afraid of lots of thin laminations.
my smartarse piece has 9 laminations for 3/4" thickness of
laminations.
bandsaw thinner laminations and add another lamination or two to make
up for the kerfs.

Stealth Pilot